The invention relates generally to shift assemblies for use in transfer cases, manual transmissions and the like and more particularly to a shift assembly for transfer cases, manual transmissions and the like having a single shift fork assembly.
In two speed transfer cases and certain manual transmissions, there is a need to shift or translate a component of speed change gearing such as a dog clutch or clutch collar from a first position which engages a first component to provide a first drive ratio and speed range through an intermediate position to a second position which provides a second, a distinct drive ratio and speed range. Frequently, such a device may also provide a selectable center or intermediate neutral position between the first and second positions. Numerous mechanical drive mechanisms intended to achieve this function have been both developed and patented.
U.S. Pat. No. 4,873,881 teaches a shift actuactor having a pair of drive motors which cooperatively provide X and Y axis movement of a shift rail.
In U.S. Pat. No. 5,150,629, a rotary actuator includes a shaft which is driven both linearly and rotatively to provide proper gear selection.
U.S. Pat. No. 5,180,959 utilizes a worm gear drive to a gear having an eccentric pin. The device includes a reaction member which provides a resilient coupling between the motor drive and shifted member.
U.S. Pat. No. 5,832,777 which is co-owned by the present assignee includes a worm gear drive which directly axially translates the shift rail and fork.
U.S. Pat. No. 5,881,853 discloses an arrangement for actuating a gear box shift mechanism which includes a circular cam driven by a worm gear.
U.S. Pat. No. 5,884,526 discloses a shift mechanism having an eccentric drive coupled to a single shift rail.
Several of the foregoing patents, while apparently providing accurate and reliable shift operation, are complex and thus problematic from manufacturing, reliability and service standpoints. The foregoing suggests that improvements in the art of single fork shift mechanisms are therefore both desirable and possible.